okay, so i'm gonna be honest with you on this.

probably a lot of why you're seeing traffic with little actual recruitment is because the vast majority of your ideal demographic (harry potter rpers in the real life medium) are 1) primarily on different resource sites like caution to the wind or a thousand fireflies or rpg-directory and 2) strongly prefer jcink as a hosting platform over proboards.

obviously, there's not a whole lot you can do about the latter issue since you can't magically change your hosting platform (pun not originally intended), but you will probably see a bit more headway to advertise in places where there's a lot more real life harry potter rpers - which, like i said, would involve putting general directory ads on those big jcink resource sites i mentioned as well as taking some time to do some more off-the-wall advertising, such as submitting ads to tumblr ad directories like rockinroleplay, therpsource, rpings, rpadverts, and allthingsroleplay; replying to site searches for hp sites on the jcink directories if your site fits fairly well for what they're looking for and doesn't have any dealbreakers for them; posting up want ads on the resource sites for general canons and/or your own personal want ads; posting up or replying to buddy searches on resource sites if the other person is okay with joining another site; or even just linking to your site in your signature on resource sites you're actively participating on. you can do some site-to-site advertising on similar genres, such as other harry potter sites or magical/school sites, but honestly, from what i've seen, most of the rl side of things tends to regard site-to-site ads as a waste of time and your returns do seem to dramatically diminish if you're advertising too far outside of your main demographic, so it's probably not as useful to you to engage in.

just doing those things alone will probably help you with membership or at least directing your efforts towards avenues where you're likely to get some nibbles.

that being said though, there are definitely some things you could do around the site to make it more attractive to potential members. if i were in your shoes, i'd probably want to redo a lot of the lore and claims threads to condense information and reduce some of the administrative concerns while simultaneously opening up the world and avoiding potential concerns about a micromanage-y or nitpicky staff. i'd also definitely recommend that you try to reword things and rework stuff in the various staff announcements in terms of the tone you're using as well - like i know that the glance i took at your rules, as a potential member, i would immediately hit the x button on a site i was considering if i came across it just because so much of the content seemed to be focused around slapping me with a ruler if i made a mistake rather than clearly outlining what the site expectations were and how things worked there. if you're a little unsure about how to rework things in that regard, i would actually suggest going through a lot of other big/popular sites in your genre (or just in general) to kind of get a feel for what the general expectations are in the community, what common rules are, and how they're all formatted and worded. i'd also probably replace the shoutbox with a site discord - they're generally more popular in rp community and you can make them guest-friendly and embeddable with bots like widgetbot or titan - or even a site cbox if you're vehemently opposed to discord, since those are the generally preferred out-of-character chatting clients (and that general site community is often just as important as anything you do with the actual site).

you're also probably struggling to pick up members because of the age-old conundrum of "members don't want to join a site that's inactive/slow but the site can't get more active if there aren't members on it to post", but again, there's not a whole lot you can do about that short of actually picking up other members and actively threading with them, so unfortunately, there's not a whole lot i can do to advise you in that regard outside of doing things like posting dev threads or oneshots or things when you can and trying to be as active as you can with other members where you can.

i can give you more specific advice in terms of things you could do to try to make the site more attractive (since this was.... honestly mostly just a drive-by for me), but honestly? i'd say you're better off trying to get suggestions and feedback from people who are much more firmly in your target demographic - after all, i could give you suggestions until the cows came home, but as someone who is largely outside of that demographic, my input is something that you should take far less seriously than feedback from people who are actively in your site genre and would actually be interested in joining your site (or would be if not for xyz factors).

anyway. i hope this is helpful for you to try to figure out where you can improve things with your site and i wish you luck with it in the future!